Method of manufacturing coated articles



Dec. 17, 1946. J. T. MULLER METHOD OF MANUFACTURING COATED ARTICLESFiled May 11, 1944 FIG. 7

/NVE/V TOP J.7.' MULLER $R,Tle' m ATTORNEY Patented Dec. 17, 1946 METHODOF MANUFACTURING COATED ARTICLES John T. Muller, Livingston, N. Jassignor to Western ElectricCompany, Incorporated, New York, N. Y., acorporation of, New York Application May 11, 1944, Serial No. 535,169

4 Claims.

This invention relates to a method of manufacturing coated articles, andmore particularly to a method of manufacturing laminar members ofbrittle crystalline material and coated on one side for use inelectrical apparatus.

The applications of slices, disks, chequers, wafers and the like usuallylaminar members of crystalline material such as quartz, silicon,graphite, carbon and the like macrocrystalline or microcrystallinesubstances coated on one fiat face with metal, in electrical arts aretoo varied and too well known to require enumeration here.

An object of the present invention is to provide a simple, reliablemethod of producing from hard and brittle material which must be shapedby abrasive agents coated laminar members particularly adapted forelectrical use, by steps which will reduce chipping and breakage to aminimum.

With the above and other objects in view, the invention may be embodiedin a method of making laminar articles having a coating on one facethereof from material shapable by abrasives which comprises steps offorming a flat smooth face on a body of the material, coating the faceso formed, cutting off a coated slice of the material by a cut parallelto the said face, coating the face of the body thus formed, a secondcoated slice by a cut parallel to the new coated face,

cementing the coated slices together to substantially reconstitute thebody, making a plurality of mutually parallel cuts in but notcompletelythrough the reconstituted body across theslices to sever these intoseparate stacks of cemented bars, making a second plurality of mutually.parallel cuts in but not completely through the reconstituted bodyacross the bars to sever these into separate stacks of cementedchequers, and treating the aggregate of chequers so formed to releasethe same from the cement.

Other objects and features will appear from the following detaileddescription of one embodiment thereof taken in connection with theaccompanying drawing, in which the same reference numerals are appliedto identical parts in the several figures and in which Fig. 1 is a viewin perspective of a parallelopipedal block of material after the firststep;

Fig. 2 is a similar View showing the result of the second step of themethod applied once;

Fig. 3 is a similar view showing the result of the'third step of themethod;

Fig. 4 is a similar view showing the result of the fourth step of themethod;

Fig. 5 is a similar view showing the result of the fifth step of themethod;

Fig. 6 is a similar view showing a single chequer as thus made;

Fig. '7 is aside-elevation of the chequer mounted for trimming;

Fig. 8 is a perspective of the mounted chequer as trimmed to form awafer; and

Fig. 9 is a perspective of a stack of chequers in a modified form of theinvention.

.As herein illustratively disclosed, the invention is embodied in amethod for manufacturingcircular disks of homogeneouslymicroscrystalline silicon, each disk having a metallic coating on onefiat face. In carrying out the method it is assumed that the silicon isat hand in parallelopipedal pieces. The first step of the processcomprises grinding one face of the silicon block 20 flat and smooth,etching thisfiat smooth face lightly to ensure its cleanliness, andcoating the smoothed and etched face electrolytically with nickel asshown at 2!. A slab 22 of predetermined thickness is sawed'from theblock by a cut parallel to the plated face. The new face'thus created onthe block is smoothed, etched and plated as before, and a second slab 22is sawed off. This procedure is repeated until all the usable portion ofthe block has been converted into slabs 22 each coated on one face withthe nickel. The blocks of silicon at present available usually have anon-homogeneous portion 23 from the bottom of the melt from which theywere made. These are then re-assembled, as shown in Fig. 3, toreconstitute the original block approximately, the slabs being cementedtogether with shellac. A series of parallel cuts is made. into thereconstituted block, perpendicular to the plurality of parallel coatedfaces of the slabs 22, which are thus converted into similarly coatedfiat bars 24 as shown in Fig. 4, and still held together by the shellaccement. .A second plurality of mutually parallel cuts is madeperpendicular to the cuts of Fig. 4 and also to the broad, coated facesof the bars. 24, thus converting the bars 24 into similarly coated,fiat, square chequers 25, as in Fig. 5. The aggregated unit shown inFig. 5, still held together by the shellac, is then separated into its.component parts by dissolving away the shellac cement, e. g., withalcohol. The cull stub 23 is disposed of. ,The product thus made is aplurality of chequers 25 like the one illustrated in Fig. 6, aparallelopipedal, small, fiat body 21 of microcrystallinesilicon with anickel coating 26 on one] of its broad faces. This product may itself bea desired one, in which case the method terminates here. For other usesthe chequers 25 may be cemented to a suitable holder 28 as shown in Fig.7 and ground peripherally to produce the circular wafer shown at 29 inFig. 8.

In the most important phase, the invention is typified by the sequenceof operations illustrated in Figs. 2, 3, 4 and 5, both the particularsteps and the order in which they are taken being important. Theimportant feature of the steps and their sequence, is that after theslabs or slices 22 of Fig. 2 have been made and re-assembled with cementas shown in Fig. 3, the object worked on as shown in Figs. 4 and 5remains a unitary'solid aggregated block. The cemented slabs of theaggregate of Fig. 3 help to support each other while the cuts shown inFig. 4 are being made; and so also the cemented bars of Fig. 4 supporteach other while the cuts shown in Fig. 5 are being made.

The crystalline materials usually in question are hard and brittle.Hence, if a single slab 22 be sawed transversely into bars 24 and if asingl bar 24 be sawed transversely into chequers 25, great care must betaken and the sawing done at relatively low speed and under relativelylight pressure, lest the material chip at the corners and edges or crackthrough the body. The same general consideration holds in respect ofother step sequences and methods of the prior art.

By the particular steps and sequence of the invention, not only are allcuts taken when the elements being out are mutually supporting eachother, but also the cement employed to hold them together is soft andresilient in comparison with the crystal substance, which appears to bean importantly useful feature in that the cement cushions the tiny butcontinuous and sharp jarring occasioned by the cutting grains of theabrasive powder or molded abrasive wheel used for the cutting. Whateverthe true theory may be, the fact is, that the method characterized bythe particularsteps and sequence of steps described, reducesvery-materially the spoilage and waste from chipping and cracking,besides enabling the cutting to be done at materially greater speed andunder materially heavier pressure than heretofore.

In a modification and extension of the method above described, the stepsand their sequence are as before until the doubly sawed block of Fig. 5

is produced. This may then be out along the planeindicated by the dottedangular line A-B in Fig. 5 to saw loose from the cull 23 stacks ofsuperimposed cemented chequers, such as the single stack generallyindicated at 32 in Fig. 9. Such a stack may be converted into a similarstack of circular wafers such as 29 in Fig. 8 by grinding off thecorners, and the wafers, then separated and cleaned by dissolving awaythe cement.

The invention has been illustrated as applied in the manufacture ofsilicon wafers coated on one face with nickel. Obviously the characterof the body as silicon specifically or of the coating as nickelspecifically, is not a limitation of the invention, which is applicableto the case of any relatively hard and brittle material which is bestformed by cutting withabrasive agents and toany coating material bothunaffected by the cement-or the cement solvent selected. The specificuse'of shellac selected here as an illustrative cement, is

also not a limitation. The manner in which the coating is applied alsois irrelevant to theinvention.

If the entire body 20 beof usable material to begin with, an artificialcull may be provided by cementing the block to another similar black orto a piece of glass or other suitable material.

Suitable apparatus to make the cuts shown in Figs. 2, 4 and 5 isdescribed in detail in copending application Serial No. 535,172, filedby the present inventor of even date herewith and which matured asPatent No. 2,382,897, .August 14, 1945; and. suitable apparatus to faceand edge trim the chequer 25 of Fig. '7 to make the wafer 29 of Fig. 8is described in detail in copending application Serial No. 535,173, alsofiled by the present inventor of even date herewith and which matured"as Patent No. 2,398,387, April 16, 1946. Apparatus to convert the prism30 of Fig. 9 into a cylinder may be anordinary lathe to hold and rotatethe prism while a grinding wheel is reciprocated lengthwise of theprism.

What is claimed is:

1. A method of making laminar articles having a coating on one facethereof from hard and brittle material shapable by abrasives whichcomprises steps of forming a fiat smooth face on a body of the material,coating the face so formed, cutting off a coated slice of the materialby a cut parallel to the said face, coating the face of the body thusformed with tough and fracture resisting substance, cutting off a secondcoated slice by a cut parallel to the new coated face, repeating thesteps of coatin a new face and cutting off an additional coated sliceuntil a desired part of the original body has been converted into coatedslices, cementing the coated slices together to substantiallyreconstitute the body, making a plurality of mutually parallel cuts inbut not completely through the reconstituted body across the slices tosever these into separate stacks of cemented bars, making a secondplurality of mutually parallel cuts in but not completely through thereconstituted body across the bars to sever these into separate stacksof cemented chequers, and treating the aggregate of chequers soformed-to release the same from the V cement.

2. A method of making laminar articles having a coating on one facethereof from hard and brittle electrically conductive mate'rialshapableby abrasives which comprises steps of forming a flat smooth face on abody of the material, coating the face so formed with metal byelectrolytic deposition, cutting off a coated slice of the material by acut parallel to the said face, coating the face of the body thusformed'with tough and fracture resisting metal by electrolyticdeposition, cutting off a secondcoated slice by a cut parallel to thenew coated face/repeating the steps of coating a new face and cuttingoff 'an additional coated slice until a desired part of the originalbody has been converted into coated slices, cementing the coated slicestogether to substantially reconstitute the body, making a plurality ofmutually parallel cuts in but not completely through the reconstitutedbody across the slices to sever these into separate stacks of cementedbars, making a second plurality of mutually parallel cuts in but notcompletely through the reconstituted body across the bars to sever theseinto-separate stacks of cemented chequers, and treating the aggregate ofchequers so formed to release the same from the cement.

3.- A method of making laminar articles having a coating on one facethereof from hard and brittle material shapable by abrasives whichcomprises steps of securing an artificial cull to a body of themateriaLforming aflat smooth face on the body, coating the 'face soformed,

cutting oil a coated slice of the material by a cut parallel to the saidface, coating the face of the body thus formed, with tough and fractureresisting substance, cutting all a second coated slice by a cut parallelto the new coated face, repeating the steps of coating new face andcutting off an additional coated slice until substantially all of theoriginal body has been converted into coated slices, cementing thecoated slices and the cull together to substantially reconstitute thebody, making a plurality of mutually parallel cuts through thereconstituted body but not completely through the cull across the slicesto sever these into separate stacks of cemented bars, making a secondplurality of mutually parallel cuts through the reconstituted body butnot completely through the cull across the bars to sever these intoseparate stacks of cemented chequers, and treating the aggregate ofchequers so formed to release the same from the cement.

4. A method of making laminar articles having a coating on one facethereof from hard and brittle electrically conductive material shapableby abrasives which comprises steps of securing an artificial cull to abody of the material, forming a flat smooth face on the body, coatingthe face so formed with metal by electrolytic deposition, cutting off acoated slice of the material by a cut parallel to the said face, coatingthe face of the body thus formed with metal by electrolytic deposition,cutting oil a second coated slice by a cut parallel to the new coatedface, repeating the steps of coating 3, new face and cutting off anadditional coated slice until substantially all of the original body hasbeen converted into coated slices, cementing the coated slices and thecull together to substantially reconstitute the body, making a pluralityof mutually parallel cuts through the reconstituted body but notcompletely through the cull across the slices to sever these intoseparate stacks of cemented bars, making a second plurality of mutuallyparallel cuts through the body but not completely through the cullacross the bars to sever these into separate stacks of cementedchequers, and treating the aggregate of chequers so formed to releasethe same from the cement.

JOHN T. MULLER.

